doc: add changelog for v2.7.

Signed-off-by: Wine93 <[email protected]>

Author: Wine93

CHANGELOG-2.7.md

@@ -0,0 +1,95 @@
+# CHANGELOG of v2.7
+
+Previous change logs can be found at [CHANGELOG-2.6](https://github.com/opencurve/curve/blob/master/CHANGELOG-2.6.md)
+
+
+## Features
+
+* [curvefs/client: add quota for S3 client](https://github.com/opencurve/curve/pull/2836), thanks to [@h0hmj][h0hmj].
+* [curvefs/client: now we support hadoop sdk](https://github.com/opencurve/curve/pull/2807), thanks to [@Wine93][Wine93].
+* [curvefs/mds: add ability to change capacity in fsinfo](https://github.com/opencurve/curve/pull/2821), thanks to [@h0hmj][h0hmj].
+* [curvefs/monitor: add memcache](https://github.com/opencurve/curve/pull/2834), thanks to [@Cyber-SiKu][Cyber-SiKu].
+* [curvefs/monitor: add cluster usage](https://github.com/opencurve/curve/pull/2842), thanks to [@Cyber-SiKu][Cyber-SiKu].
+* [curvefs/monitor: support plugin](https://github.com/opencurve/curve/pull/2830), thanks to [@Cyber-SiKu][Cyber-SiKu].
+* [curvefs/docker: support run curvefs on Openeuler 22.03-lts-sp2 platform](https://github.com/opencurve/curve/pull/2789), thanks to [@peter5232][peter5232].
+* [curvebs/chunkserver: support format chunkfile pool in asynchronous](https://github.com/opencurve/curve/pull/2775), thanks to [@Vigor-jpg][Vigor-jpg].
+
+## Improve
+
+* [curvefs/client: optimizing the read amplification problem, especially for memcache](https://github.com/opencurve/curve/pull/2792), thanks to [@wuhongsong][wuhongsong].
+* [curvefs/client: split latency metric into data and attr](https://github.com/opencurve/curve/pull/2824), thanks to [@Cyber-SiKu][Cyber-SiKu].
+* [curvefs/mds: support modify some configs on fly](https://github.com/opencurve/curve/pull/2813), thanks to [@Cyber-SiKu][Cyber-SiKu].
+* [curvefs/metaserver: remove some unnecessary error logs](https://github.com/opencurve/curve/pull/2831), thanks to [@SeanHai][SeanHai].
+* [build: install clang-format-14 in dev docker](https://github.com/opencurve/curve/pull/2828), thanks to [@wu-hanqing][wu-hanqing].
+* [build: add braft format patch](https://github.com/opencurve/curve/pull/2661), thanks to [@wu-hanqing][wu-hanqing].
+* [build: support build specified library](https://github.com/opencurve/curve/pull/2829), thanks to [@quas-modo][quas-modo].
+* [doc: updated maintainers for curve project](https://github.com/opencurve/curve/pull/2695), thanks to [@aspirer][aspirer].
+
+
+## Bugfix
+
+[Cyber-SiKu]: https://github.com/Cyber-SiKu
+[h0hmj]: https://github.com/h0hmj
+[wu-hanqing]: https://github.com/wu-hanqing
+[Wine93]: https://github.com/Wine93
+[Vigor-jpg]: https://github.com/Vigor-jpg
+[SeanHai]: https://github.com/SeanHai
+[quas-modo]: https://github.com/quas-modo
+[wuhongsong]: https://github.com/wuhongsong
+[peter5232]: https://github.com/peter5232
+[aspirer]: https://github.com/aspirer
+
+# Performance
+
+## Hardware
+3 nodes (3*mds, 9*metaserver), each with:
+ - Intel(R) Xeon(R) CPU E5-2680 v4 @ 2.40GHz
+ - 256G RAM
+ - disk cache: INTEL SSDSC2BB80 800G (IOPS is about 30000+, bandwidth is about 300 MiB)
+
+## Configure
+
+```yaml
+fs.cto: true
+fs.lookupCache.negativeTimeoutSec: 1
+fs.lookupCache.minUses: 3
+fuseClient.supportKVcache: true
+client.loglevel: 0
+```
+
+## fio
+
+```bash
+[global]
+rw=randread
+direct=1
+size=50G
+iodepth=128
+ioengine=libaio
+bsrange=4k-4k
+ramp_time=10
+runtime=300
+group_reporting
+
+[disk01]
+filename=/path/to/mountpoint/1.txt
+```
+
+| fio | IOPS/bandwidth | avg-latency(ms) | clat 99.00th (ms) | clat 99.99th (ms) |
+| :----: | :----: | :----: | :----: | :----: |
+| numjobs=1 / size=50GB / 4k randwrite | 4243      | 0.23 | 0.176 | 2   |
+| numjobs=1 / size=50GB / 4k randwrite | 908       | 1.0  | 3.5   | 104 |
+| numjobs=1 / size=50GB / 512k write   | 412 MiB/s | 2.4  | 19    | 566 |
+| numjobs=1 / size=50GB / 512k read    | 333 MiB/s | 2.9  | 20    | 115 |
+
+## mdtest
+
+```bash
+for i in 1 4 8; do mpirun --allow-run-as-root -np $i mdtest -z 2 -b 3 -I 10000 -d /path/to/mountpoint; done
+```
+
+| Case | Dir creation | Dir stat | Dir removal | File creation | File stat | File read | File removal | Tree creation | Tree removal |
+| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
+| client*1 | 341 | 395991 | 291 | 334 | 383844 | 3694 | 309 | 322 | 851 |
+| client*4 | 385 | 123266 | 288 | 361 | 1515592 | 15056 | 310 | 363 | 16 |
+| client*8 | 415 | 22138 | 314 | 400 | 2811416 | 20976 | 347 | 355 | 8 |